Electrochemical sensors are used in detecting and measuring the presence and amount of selected gas present in ambient atmosphere or work environment. Generally, these sensors are well known and utilize various electrode, electrolyte and solvent combinations which are known to be selectively sensitive to a desired gas or gases. These gases are usually introduced to the sensor by diffusion through a gas porous membrane, for example, a membrane made of sintered tetrafluoroethylene. The gas is either reduced or oxidized by the cell creating an electrochemical signal proportional to gas component in the sample area.
During the operation of the electrochemical sensors, the solvent, for example sulfuric acid or a non-aqueous organic solvent such as propylene carbonate, is lost through evaporation or permeation. This loss results in a decrease in the life of the sensor. One method of reducing the loss of solvent is place a means for humidifying the stream of gases directed to the sensor membrane. While the humidifier reduces evaporative losses and in some cases replaces lost aqueous solvents, the addition of such equipment greatly increases the size of the equipment. This size increase can be accepted in stationary equipment, but is generally unacceptable in portable monitoring type sensing equipment. Also, it has been found that adding humidity to the flow stream is not acceptable in times of low temperatures where the water can freeze resulting in a possible humidifier failure.
Another solution is to store the sensor device during nonuse in a chamber filled with vapors of the solvent. This solution is more practicable for portable sensor devices than for permanent monitoring type devices which are mounted at fixed locations or very large in size.
It is an object of the present invention to provide a device for replenishing the solvent which is adaptable to both permanent sensing monitors and portable sensing monitors. It is a further object to provide a device for replenishing the solvent of an electrochemical sensor which is convenient to use.